Back-light

ABSTRACT

A liquid crystal display device includes a plurality of light source packages each having a light-emitting portion for emitting light, a light guide plate which light emitted from the light source packages enters through the incidence surface, having a height and a width, and from which the light exits through the exit surface, and a liquid crystal display panel for controlling, for each pixel, the orientation of a liquid crystal material to control the transmission of the light exiting through the exit surface. Each light source package has two opposing long sides and two opposing short sides when viewed from the direction of the light emitted by the light-emitting portion. The plurality of light source packages are arranged long side to long side in the direction along the width.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese applicationJP2014-114228 filed on Jun. 2, 2014, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid crystal display device.

2. Description of the Related Art

Liquid crystal display devices are widely used as display devices intelevisions or information communication terminals such as computers.Such a liquid crystal display device is configured to change theorientation of a liquid crystal material sandwiched between twosubstrates by changes in an electric field, thus controlling thetransmission of light passing through these two substrates and theliquid crystal material to produce images.

In such a liquid crystal display device, it is common to use a lightingdevice called a “backlight” as a light source. As backlighting systems,a direct-lit backlight, which has light sources behind a liquid crystaldisplay surface, and an edge-lit (side-lit) backlight, which illuminatesa liquid crystal display surface by reflecting light emitted from theside, are typically known. The liquid crystal display devices used inrecent mobile communication terminals, such as smartphones, are requiredto be made smaller and consume less power. Thus, the edge-lit backlightsincluding light emitting diodes (LEDs) as light sources have come intouse.

JP 2014-029798 A discloses a lighting device with an edge-lit backlightthat can enhance the efficiency of providing light to a light guideplate to reduce the thickness of the lighting device.

In the above edge-lit backlight, light sources such as LEDs are arrangedalong any one or more of the four sides of the screen. If more lightsources were arranged to increase the brightness, the frame area formedaround the display area would be wider to make the display devicelarger.

SUMMARY OF THE INVENTION

In view of the above circumstances, it is an object of the presentinvention to provide a liquid crystal display device that can increasethe brightness without widening the frame area.

Exemplary liquid crystal display devices to solve the above problems areas follows.

(1) A liquid crystal display device includes a plurality of light sourcepackages each having a light-emitting portion for emitting light, alight guide plate which light emitted from the light source packagesenters through the incidence surface, having a height and a width, andfrom which the light exits through the exit surface, and a liquidcrystal display panel for controlling, for each pixel, the orientationof a liquid crystal material to control the transmission of the lightexiting through the exit surface. Each light source package has twoopposing long sides and two opposing short sides when viewed from thedirection of the light emitted by the light-emitting portion. Theplurality of light source packages are arranged long side to long sidein the direction along the width.

(2) In the liquid crystal display device according to the above (1), thecenter of the light-emitting portion may be located at a position thatdoes not overlap with a centerline connecting the midpoints of the longsides of the light source package when viewed from the direction of theemitted light, and the plurality of light source packages may bearranged so that a light source centerline connecting the centers of thelight-emitting portions overlaps with a light guide plate centerlineindicating half the height of the incidence plane when viewed from thedirection of the emitted light.

(3) In the liquid crystal display device according to the above (1), thedirection in which the long sides of each of the plurality of lightsource packages extend may be oblique to the direction along the heightof the incidence plane.

(4) In the liquid crystal display device according to the above (1) or(3), the plurality of light source packages may be arranged in thedirection along the width so that the light source packages having thelight-emitting portion in one side thereof in the direction along theheight alternate with the light source packages having thelight-emitting portion in the other side.

(5) In the liquid crystal display device according to the above (1), theplurality of light source packages may each have a plurality of thelight-emitting portions arranged therein, and the center of gravity of ashape having the centers of the plurality of light-emitting portions asvertexes may be arranged at the same level as half the height of theincidence plane of the light guide plate when viewed from the directionof the emitted light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing a liquid crystal displaydevice according to an embodiment of the present invention;

FIG. 2 is a diagram schematically showing a cross section of a lowerframe, a backlight unit, and a liquid crystal display panel;

FIG. 3 is a diagram showing a layout of a plurality of light sourcepackages arranged on a package-arranging plate;

FIG. 4 is a diagram showing an arrangement of a light-emitting portionin the light source package;

FIG. 5 is a diagram illustrating a layout of the plurality of lightsource packages, which are arranged on the package-arranging plate toincline at an angle of 30° to the height direction of a light guideplate;

FIG. 6 is a diagram illustrating a layout of the plurality of lightsource packages, which are arranged on the package-arranging plate toincline at an angle of 45° to the height direction of the light guideplate;

FIG. 7 is a diagram illustrating a modified arrangement of the lightsource packages arranged on the package-arranging plate; and

FIG. 8 is a diagram illustrating another modified arrangement of thelight source packages arranged on the package-arranging plate.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described below with referenceto the accompanying drawings. The disclosure herein is merely anexample, and appropriate modifications coming within the spirit of thepresent invention, which are easily conceived by those skilled in theart, are intended to be included within the scope of the invention as amatter of course. The accompanying drawings schematically illustratewidths, thicknesses, shapes, or other characteristics of each part forclarity of illustration, compared to actual configurations. However,such a schematic illustration is merely an example and not intended tolimit the present invention. In the present specification and drawings,some elements identical or similar to those shown previously are denotedby the same reference signs as the previously shown elements, and thusrepetitive detailed descriptions of them may be omitted as appropriate.

FIG. 1 schematically shows a liquid crystal display device 100 accordingto an embodiment of the present invention. As shown in the diagram, theliquid crystal display device 100 includes a liquid crystal displaypanel 150, a mold frame 101 fixing the liquid crystal display panel 150,a backlight unit 200 that illuminates the liquid crystal display panel150 from behind, and a lower frame 102 housing the backlight unit 200.The liquid crystal display panel 150 controls the orientation of aliquid crystal material sandwiched between two substrates to control thetransmission of light. Such a configuration is shown in this embodiment,whereas only a frame or other housings without the mold frame 101 mayhouse both the liquid crystal display panel 150 and the backlight unit200. The liquid crystal display panel 150 may be a well-known orsuitable liquid crystal display panel that controls the orientation of aliquid crystal material by what is called an in-plane switching (IPS) orother systems.

FIG. 2 is a diagram schematically showing a cross section of the lowerframe 102, the backlight unit 200, and the liquid crystal display panel150. As shown in the diagram, the backlight unit 200 includes aplurality of light source packages 220, a package-arranging plate 216, alight guide plate 210, and an optical sheet 204. The light sourcepackages 220 have as light sources, for example, LEDs that emit whitelight. The plurality of light source packages 220 are arranged on thepackage-arranging plate 216. The light emitted from the light sourcepackages 220 enters the light guide plate 210 through an incidencesurface 212 and exits through an exit surface 214 as planar light. Theoptical sheet 204 is formed of prism sheets stacked on the exit surface214 and a diffuser sheet. The backlight unit 200 is disposed in thelower frame 102. The liquid crystal display panel 150 is disposed on theoptical sheet 204 of the backlight unit 200. Here, the composition ofthe optical sheet 204 may be modified as appropriate. Alternatively,other configuration without the optical sheet 204 may be employed. Thebacklight unit 200 may have a reflective sheet, which reflects lighttending to exit the light guide plate 210 through the bottom, under thelight guide plate 210. In this embodiment, the light source packages 220are arranged so that the direction of the light emitted from the lightsource packages 220 is perpendicular to the incidence surface 212 of thelight guide plate 210. Alternatively, the direction of the light emittedfrom the light source packages 220 may be oblique to the incidencesurface 212 of the light guide plate 210.

FIG. 3 is a diagram showing a layout of the plurality of light sourcepackages 220 arranged on the package-arranging plate 216 when viewedfrom the direction of the light emitted from the light source packages220. In this diagram, the outline of the incidence surface 212 of thelight guide plate 210 is indicated by two-dot chain lines to show thepositional relationship between the light source packages 220 and thelight guide plate 210. The light source packages 220 are each what iscalled a chip LED, which includes, for example, an LED device, asubstrate including a circuit coupled to the LED device by wire bonding,a resin containing a phosphor and covering the LED device, and anode andcathode electrodes for coupling to an external circuit. The light sourcepackage 220 can be selected from among well-known or suitable chip LEDs.

As shown in FIG. 3, the light source packages 220 each have arectangular face with two long sides and two short sides, and areattached to the package-arranging plate 216 so as to be arranged longside to long side. As shown in FIG. 4, the center 288 of alight-emitting portion 221 of the light source package 220 is located ata position that does not overlap with a centerline 402 connecting themidpoints of the long sides of the light source package 220. That is,the centerline 402 of the light source package 220 is arranged in aposition different from a light source centerline 401 connecting thecenters of the light-emitting portions 221. The light-emitting portion221 is a portion that actually emits light, where the LED device isdisposed in this case. The center of the light-emitting portion 221 maybe the center of gravity of the light-emitting portion 221 when viewedfrom the direction of the light emitted from the light source package220. In this embodiment, as shown in FIG. 3, the light source centerline401 is arranged to overlap with a light guide plate centerline 301,which is the centerline indicating half the height of the light guideplate 210. The height of the light guide plate 210 here is the lengthextending in the direction perpendicular to the exit surface 214 of thelight guide plate 210, and the width is the length extending in thedirection perpendicular to the height on the incidence surface 212.

Thus, the plurality of light source packages 220 are arranged long sideto long side with each other in the width direction. Therefore, a largernumber of light source packages 220 can be arranged along one side toincrease the brightness of the backlight unit 200 without widening theframe area. Even when the plurality of light source packages 220 arearranged long side to long side, the center of the emitted light isincident on the incidence surface 212 of the light guide plate 210 athalf the height of the surface. This arrangement can enhance the useefficiency of the light. In addition, this arrangement can reduce thenumber of package-arranging plates 216, which are arranged along sidesof the display area.

In FIG. 3, the light source packages 220 are arranged so that the longsides of the light source packages 220 are directed in the heightdirection of the light guide plate 210. Alternatively, the long sides ofthe light source packages 220 may be directed obliquely as shown inFIGS. 5 and 6, for example, when the package-arranging plate 216 or thelight guide plate 210 is limited in height. Also in this case, the lightsource centerline 401 can be arranged to overlap with the light guideplate centerline 301 of the light guide plate 210. FIG. 5 is a diagramshowing an example where the light source packages 220 are inclined atan angle of 30° to the height direction of the light guide plate 210.FIG. 6 is a diagram showing an example where the light source packages220 are inclined at an angle of 45° to the height direction of the lightguide plate 210. Thus, the direction in which the long sides of thelight source packages 220 extend is oblique to the height direction ofthe incidence surface 212. This can enhance the use efficiency of lightas well as arrange the light source packages 220 for the light guideplate 210 having a smaller thickness (height) or for thepackage-arranging plate 216 having a lower height. The configurationsshown in FIGS. 5 and 6 can also produce the same effects as thosedescribed in the above embodiment.

FIG. 7 is a diagram illustrating a modified arrangement of the lightsource packages 220 arranged on the package-arranging plate 216. Asillustrated in the diagram, in each light source package 220, the center288 of the light-emitting portion 221 is located at a position that doesnot overlap with the centerline 402 connecting the midpoints of the longsides of the light source package 220, as in the above embodiment. Here,the plurality of light source packages 220, each having thelight-emitting portion 221 in one of two sides (halves) thereof in thelong side direction, are arranged long side to long side so that thosehaving the light-emitting portion 221 in one side (upper half) alternatewith those having the light-emitting portion 221 in the other side(lower half). Such an arrangement can cause a light source centerline501, which is the longitudinal centerline of the combination of theplurality of light source packages 220, to overlap with half the heightof the light guide plate 210 to enhance the use efficiency of light, forexample, even when the light source centerline 401 cannot be arranged tooverlap with the light guide plate centerline 301 in the arrangement asshown in FIG. 3 because of structural reasons. Such a modification canalso produce the same effects as those described in the aboveembodiment.

FIG. 8 is a diagram illustrating another modified arrangement of thelight source packages 220 arranged on the package-arranging plate 216.As illustrated in the diagram, the light source packages 220 accordingto this modification each have two light-emitting portions 221. In thiscase, the midpoints of the line segment joining the centers 288 of thetwo light-emitting portions 221 of individual light source packages 220can be determined as centers that become a reference of a light sourcecenterline, and the line connecting these centers can be defined as alight source centerline 502. Even for such light source packages 220,the use efficiency of light can be enhanced by arranging the light guideplate 210 so that the light source centerline 502 overlaps with thelight guide plate centerline 301 when viewed from the direction of thelight emitted from the light-emitting portions 221. Whereas the lightsource packages 220 each have two light-emitting portions 221 in thismodification, they may each have three or more. In such a case, thecenter of gravity of the shape that has the centers of the plurality oflight-emitting portions 221 as its vertexes can be defined as centersthat become a reference of a light source centerline. Such amodification can also produce the same effects as those described in theabove embodiment.

In the above embodiment, half the height of the light guide plate 210,which is defined as the light guide plate centerline 301, is determinedto be at the same level as the center of incident light. Alternatively,the position where the use efficiency of the incident light is maximizedmay be determined as the light guide plate centerline 301, when the useefficiency of the incident light is not maximized at half the height ofthe light guide plate 210 as a result of using a reflective sheet or thelike spread on the lower frame 102 side of the light guide plate 210.

In the above embodiment, LEDs are used as the light sources.Alternatively, other self-luminous light-emitting devices may be used.Whereas the backlight unit 200 in the above embodiment is used for theliquid crystal display device, it may be used for display devicesemploying micro electro mechanical systems (MEMS) or other displaydevices.

While there have been described what are at present considered to becertain embodiments of the invention, it will be understood that variousmodifications may be made thereto, and it is intended that the appendedclaims cover all such modifications as fall within the true spirit andscope of the invention.

What is claimed is:
 1. A back-light comprising: a plurality of lightsource packages each having a plurality of light-emitting portions foremitting light; and a light guide plate including an incident planehaving a height and a width, and an exit plane, the light emitted fromthe light source packages being incident on the incident plane andexiting through the exit plane, wherein the incident plane and the exitplane are nonparallel to each other, each of the light source packageshas two opposing long sides and two opposing short sides when viewedfrom a direction of the light emitted from the plurality oflight-emitting portions, the plurality of light source packages arearranged side by side in a direction along the width, the plurality oflight-emitting portions of each of the plurality of light sourcepackages are arranged in a direction along the two opposing long sidesand face the incident plane, and the two opposing long sides extendalong the height direction of the incident plane.
 2. The back-lightaccording to claim 1, wherein the plurality of light-emitting portionshave respective center points that are vertexes of a shape, the shapehaving a center of gravity at the same level as half of the height ofthe incident plane of the light guide plate when viewed from thedirection of the emitted light.
 3. A back-light comprising: a pluralityof light source packages each having a light-emitting plane; and a lightguide plate including an incident plane having a height and a width, andan exit plane, light emitted from the light source packages beingincident on the incident plane and exiting through the exit plane,wherein the incident plane and the exit plane are nonparallel to eachother, the light-emitting plane has a plurality of light-emittingportions arranged therein for emitting the light, and two opposing longsides and two opposing short sides when viewed from a direction of thelight emitted from the plurality of light-emitting portions, theplurality of light source packages are arranged side by side in adirection along the width so that the light-emitting plane faces theincident plane, the plurality of light-emitting portions of each of theplurality of light source packages are arranged in a direction along thetwo opposing long sides, and the two opposing long sides extend obliqueto the height direction of the incident plane.
 4. The back-lightaccording to claim 3, wherein the plurality of light-emitting portionshave respective center points that are vertexes of a shape, the shapehaving a center of gravity at the same level as half of the height ofthe incident plane of the light guide plate when viewed from thedirection of the emitted light.
 5. A back-light comprising: a pluralityof light source packages each having a light-emitting plane and twolight-emitting portions arranged in the light-emitting plane foremitting light; and a light guide plate including an incident planehaving a height and a width, and an exit plane, light emitted from thelight source packages being incident on the incident plane and exitingthrough the exit plane, wherein the incident plane and the exit planeare nonparallel to each other, the light-emitting plane has two opposinglong sides and two opposing short sides when viewed from a direction ofthe light emitted from the two light-emitting portions, the plurality oflight source packages are arranged side by side in a direction along thewidth, the two light-emitting portions of each of the plurality of lightsource packages are arranged in a direction along the two opposing longsides, the light-emitting plane faces the incident plane, and the twoopposing long sides extend oblique to the height direction of theincident plane.
 6. The back-light according to claim 5, wherein the twolight-emitting portions have respective center points that are vertexesof a shape, the shape having a center of gravity at the same level ashalf of the height of the incident plane of the light guide plate whenviewed from the direction of the emitted light.